Burke Jl

Inter-relationships among alternative definitions of feed efficiency in grazing lactating dairy cows.

International interest in feed efficiency, and in particular energy intake and residual energy intake (REI), is intensifying due to a greater global demand for animal-derived protein and energy sources. Feed efficiency is a trait of economic importance, and yet is overlooked in national dairy cow breeding goals. This is due primarily to a lack of accurate data on commercial animals, but also a lack of clarity on the most appropriate definition of the feed intake and utilization complex. The objective of the present study was to derive alternative definitions of energetic efficiency in grazing lactating dairy cows and to quantify the inter-relationships among these alternative definitions. Net energy intake (NEI) from pasture and concentrate intake was estimated up to 8 times per lactation for 2,693 lactations from 1,412 Holstein-Friesian cows. Energy values of feed were based on the French Net Energy system where 1 UFL is the net energy requirements for lactation equivalent of 1kg of air-dry barley. A total of 8,183 individual feed intake measurements were available. Energy balance was defined as the difference between NEI and energy expenditure. Efficiency traits were either ratio-based or residual-based; the latter were derived from least squares regression models. Residual energy intake was defined as NEI minus predicted energy to fulfill the requirements for the various energy sinks. The energy sinks (e.g., NEL, metabolic live weight) and additional contributors to energy kinetics (e.g., live weight loss) combined, explained 59% of the variation in NEI, implying that REI represented 41% of the variance in total NEI. The most efficient 10% of test-day records, as defined by REI (n=709), on average were associated with a 7.59 UFL/d less NEI (average NEI of the entire population was 16.23 UFL/d) than the least efficient 10% of test-day records based on REI (n=709). Additionally, the most efficient 10% of test-day records, as defined by REI, were associated with superior energy conversion efficiency (ECE, i.e., NEL divided by NEI; ECE=0.55) compared with the least efficient 10% of test-day records (ECE=0.33). Moreover, REI was positively correlated with energy balance, implying that more negative REI animals (i.e., deemed more efficient) are expected to be, on average, in greater negative energy balance. Many of the correlations among the 14 defined efficiency traits differed from unity, implying that each trait is measuring a different aspect of efficiency.

Effects of application in spring of urea fertiliser on aspects of reproductive performance of pasture-fed dairy cows

Abstract AIMS: To assess if raising concentrations of crude protein (CP) in pasture in spring by the frequent application of urea fertiliser would affect ovarian follicular dynamics, luteal function, onset of oestrus and reproductive performance of dairy cows under farming conditions in New Zealand. METHODS: Spring-calved dairy cows were grazed for 101 days in paddocks that were either not fertilised (Control; n=20) during the course of the study, or were fertilised with 40–50 kg nitrogen (N)/ha every 4–6 weeks (High-N; n=20). Similar generous pasture allowances were offered to both groups. Concentrations of CP in pasture, urea in serum and progesterone in milk were measured. Ovarian follicular and luteal dynamics were determined using ultrasonography. Oestrous behaviour and the number, time and outcome of inseminations were also recorded. RESULTS: Mean concentrations of CP in pasture and urea in serum was higher in the High-N than the Control group (25.2 vs21.6 and 8.3 vs 5.4 mmol/L for CP and urea, respectively; p<0.001). Intervals between calving and first oestrus, first insemination and conception, the time of first emergence of a dominant follicle, milk progesterone concentration, and the diameter of the corpus luteum (CL) in the first luteal phase did not differ significantly between groups. The interval from calving to first ovulation tended (p=0.10) to be lower and the diameter of the dominant follicle of the oestrous cycle at which cows conceived was greater (p=0.02) in Control than High-N cows. CONCLUSIONS: The use of large amounts of urea fertiliser during spring and the consequent increases in concentrations of CP in pasture and urea in serum did not negatively affect any of the parameters of reproductive performance of pasture-fed dairy cows that were assessed in this study.

A comparison of growth, carcass, and meat characteristics of Jersey‐ and Friesian‐cross heifers in a once‐bred heifer system of beef production

Abstract This two‐year study compared growth, carcass, and meat quality characteristics of 57 Hereford × Friesian (H × F) and 45 Hereford × Jersey (H × J) heifers in a Once‐Bred Heifer (OBH) beef production system. Liveweights for the H × J group at mating, pre‐calving, weaning, and final weighing were 26.5 kg, 22 kg, 35 kg, and 37 kg lighter, respectively, than the H × F group. Birth weights of calves from H × J heifer dams were significantly lighter than for H × F dams. Hereford × Jersey heifers had significantly lighter carcass weights, but similar weight‐adjusted dressing‐out percentages. At a common carcass weight, H × J carcasses had significantly heavier kidney and pelvic fat, greater fat depths over the eye muscle between ribs 12 and 13, and lower carcass weight‐adjusted femur bone weights. At the same carcass weight, the weights of three major hindquarter cuts were heavier for the H × F group, but the ratio of the combined weight of these cuts to femur bone weight was significantly lower for that...

Genetics of alternative definitions of feed efficiency in grazing lactating dairy cows

The objective of the present study was to estimate genetic parameters across lactation for measures of energy balance (EB) and a range of feed efficiency variables as well as to quantify the genetic inter-relationships between them. Net energy intake (NEI) from pasture and concentrate intake was estimated up to 8 times per lactation for 2,481 lactations from 1,274 Holstein-Friesian cows. A total of 8,134 individual feed intake measurements were used. Efficiency traits were either ratio based or residual based; the latter were derived from least squares regression models. Residual energy intake (REI) was defined as NEI minus predicted energy requirements [e.g., net energy of lactation (NEL), maintenance, and body tissue anabolism] or supplied from body tissue mobilization; residual energy production was defined as the difference between actual NEL and predicted NEL based on NEI, maintenance, and body tissue anabolism/catabolism. Energy conversion efficiency was defined as NEL divided by NEI. Random regression animal models were used to estimate residual, additive genetic, and permanent environmental (co)variances across lactation. Heritability across lactation stages varied from 0.03 to 0.36 for all efficiency traits. Within-trait genetic correlations tended to weaken as the interval between lactation stages compared lengthened for EB, REI, residual energy production, and NEI. Analysis of eigenvalues and associated eigenfunctions for EB and the efficiency traits indicate the ability to genetically alter the profile of these lactation curves to potentially improve dairy cow efficiency differently at different stages of lactation. Residual energy intake and EB were moderately to strongly genetically correlated with each other across lactation (genetic correlations ranged from 0.45 to 0.90), indicating that selection for lower REI alone (i.e., deemed efficient cows) would favor cows with a compromised energy status; nevertheless, selection for REI within a holistic breeding goal could be used to overcome such antagonisms. The smallest (8.90% of genetic variance) and middle (11.22% of genetic variance) eigenfunctions for REI changed sign during lactation, indicating the potential to alter the shape of the REI lactation profile. Results from the present study suggest exploitable genetic variation exists for a range of efficiency traits, and the magnitude of this variation is sufficiently large to justify consideration of the feed efficiency complex in future dairy breeding goals. Moreover, it is possible to alter the trajectories of the efficiency traits to suit a particular breeding objective, although this relies on very precise across-parity genetic parameter estimates, including genetic correlations with health and fertility traits (as well as other traits).

Milk production of Holstein-Friesian, Jersey and crossbred cows milked once-a-day or twice-a-day in New Zealand

ABSTRACT The objective of this study was to compare Holstein-Friesian (F), Jersey (J) and crossbred (F × J) cows milked once-a-day (OAD) or twice-a-day (TAD) in New Zealand for milk, fat and protein yield, lactation persistency and average somatic cell score (SCS). Data consisted of 223,149 herd-test records (89,297 and 133,852 OAD and TAD, respectively) from 11,848 F; 11,677 J and 27,720 F × J spring-calving cows between 2008 and 2012. Compared to TAD systems, cows milked OAD yielded 722, 28.0 and 22.2 kg less milk, fat and protein, respectively. Crossbred and J cows were less affected than F cows by OAD milking with a reduction in milk yield traits of ≤ 19.0%, while in F cows the reduction ranged between 19%–25%. Cows milked OAD had higher SCS than cows milked TAD (6.20 vs. 6.08). The greatest SCS difference in OAD and TAD systems was in first-lactation cows (6.40 vs. 6.02). Persistency of production traits was greater in F and F × J cows milked OAD than in F and F × J cows milked TAD, but J cows had similar milk and protein persistency in both systems. Overall, cows milked OAD had greater persistency than cows milked TAD (79%–90% vs. 76%–85%). These results show that, in commercial herds, the relative difference in production traits between OAD and TAD systems was smaller than those reported in experimental trials.

Comparative performance in Holstein-Friesian, Jersey and crossbred cows milked once daily under a pasture-based system in New Zealand

ABSTRACT Production and efficiency of Holstein-Friesian (F), Jersey (J) and crossbred F × J milked once-a-day (OAD) were studied at Massey University dairy farm No. 1. Herd test records of milk yields, somatic cell score (SCS), live weight (LW) and body condition score (BCS) were used to model the lactation curves using a third-order orthogonal polynomial. Total lactation yields of milk (MY), fat (FY), protein (PY) and milk solids (MS = FY + PY) were calculated based on predicted daily yields. Predicted efficiencies were feed conversion efficiency (FCE; total lactation MS per kg of predicted total lactation dry matter intake [DMI]); biological efficiency (BE; total lactation MS per 100 kg of LW) and DMI capacity (DMIC; total lactation DMI per 100 kg of LW). Holstein-Friesian cows yielded 376 kg milk more than F × J cows and 1101 kg milk more than J cows per lactation. Holstein-Friesian and F × J produced similar total lactation MSY (366 and 369 kg, respectively). Jersey cows were more efficient than cows of the other breeds: FCE was 78.2, 82.3 and 86.3; BE was 69.7, 74.1 and 77.8; and DMIC was 887.9, 896.8 and 897.7 for F, F × J and J cows, respectively. There were significant differences in production and efficiency among the breeds, with J cows being more efficient per 100 kg of LW than F or F × J cows. Further research is required to compare breed profit per ha in order to conclude the best breed for OAD systems.

Growth, feed intake and maternal performance of Angus heifers selected for high or low growth and milk production

Weight of calf weaned per cow that incorporates both growth and maternal component traits is an important determinant of profitability for cow–calf production systems. In New Zealand, there is little objective information available on the performance of progeny from bulls selected for either growth or maternal ability when compared under similar pastoral farming conditions. The present experiment produced 84 Angus heifers sired by Angus bulls divergently selected for high (Hi-Gr) or low (Lo-Gr) estimated breeding value (EBV) 600-day weight or high (Hi-Milk) or low (Lo-Milk) 200-day maternal EBV. Each heifer had their liveweight gain from weaning to just before first calving, herbage intake from pasture using the n-alkane method, and maternal performance (calf production after first and second parity) assessed. Liveweights of heifers born to Hi-Gr bulls were generally greater than for all other lines, while there was no difference between Lo-Gr and either of the maternal lines. There was no difference (P > 0.05) in herbage intake between the different genetic lines when measured at Days 310 (days of age from birth) and 880. At Day 400, the Lo-Milk selection line had higher (P < 0.05) intakes than the Hi-Milk, Hi-Gr and Lo-Gr lines. Calves born to the Lo-Gr heifers at the first parity were lighter while the birth weights of calves born at the second parity calving were similar for all the selection lines. Calf weaning weight was lowest (P < 0.05) after both the first and second parity weaning for the Lo-Milk sired heifers. The Lo-Milk heifers produced the least milk at Day 50 during their first lactation while the Hi-Milk heifers produced the most. This experiment confirms that for beef cattle, producers who wish to select bulls to use in their herds based on either high growth rate or high milk EBV, the resultant progeny will outperform those that are average or below average for those particular traits.

Characteristics of feed efficiency within and across lactation in dairy cows and the effect of genetic selection

The objective of the present study was to investigate the phenotypic inter- and intra-relationships within and among alternative feed efficiency metrics across different stages of lactation and parities; the expected effect of genetic selection for feed efficiency on the resulting phenotypic lactation profiles was also quantified. A total of 8,199 net energy intake (NEI) test-day records from 2,505 lactations on 1,290 cows were used. Derived efficiency traits were either ratio based or residual based; the latter were derived from least squares regression models. Residual energy intake (REI) was defined as NEI minus predicted energy requirements based on lactation performance; residual energy production (REP) was defined as net energy for lactation minus predicted energy requirements based on lactation performance. Energy conversion efficiency was defined as net energy for lactation divided by NEI. Pearson phenotypic correlations among traits were computed across lactation stages and parities, and the significance of the differences was determined using the Fisher r-to-z transformation. Sources of variation in the feed efficiency metrics were investigated using linear mixed models, which included the fixed effects of contemporary group, breed, parity, stage of lactation, and the 2-way interaction of parity by stage of lactation. With the exception of REI, parity was associated with all efficiency and production traits. Stage of lactation, as well as the 2-way interaction of parity by stage of lactation, were associated with all efficiency and production traits. Phenotypic correlations among the efficiency and production traits differed not only by stage of lactation but also by parity. For example, the strong phenotypic correlation between REI and energy balance (EB; 0.89) for cows in parity 3 or greater and early lactation was weaker for parity 1 cows at the same lactation stage (0.81), suggesting primiparous cows use the ingested energy for both milk production and growth. Nonetheless, these strong phenotypic correlations between REI and EB suggested negative REI animals (i.e., more efficient) are also in more negative EB. These correlations were further supported when assessing the effect on phenotypic performance of animals genetically divergent for feed intake and efficiency based on parental average. Animals genetically selected to have lower REI resulted in cows who consumed less NEI but were also in negative EB throughout the entire lactation. Nonetheless, such repercussions of negative EB do not imply that selection for negative REI (as defined here) should not be practiced, but instead should be undertaken within the framework of a balanced breeding objective, which includes traits such as reproduction and health.

Genotype-by-milking frequency interaction for milk production traits in New Zealand

ABSTRACT The objective of this study was the estimation of genetic correlation (rg) for milk production traits across milking frequency (MF) in New Zealand dairy cattle milked once-(OAD) or twice-a-day (TAD). Analysis was made of lactation yields of milk, fat and protein, and somatic cell score of Holstein-Friesian (F), Jersey (J) and crossbred F × J breed populations cows herd-tested between 2008 to 2012 while in their first and second lactations. The estimates of rg were, in general, greater than 0.80, providing no evidence of a genotype-by-milking frequency (G × MF) interaction. Genetic correlations tended to be greater in second compared to first lactation cows and greater in J compared to F and F × J breed populations. The results also indicate a scaling effect, due to differences in the genetic variances across breed populations and MF, with the variances being lower in the OAD population. The results demonstrate that there is no need for a separate selection scheme for the OAD milking cow population, as long as there is similarity between breeding objectives and selection indices for both MF systems. The scaling effect indicates that the best animals in TAD system would also perform the best under OAD but genetic progress is expected to be lower in OAD compared to TAD systems because lower genetic variances in breed populations milked OAD.

Factors that influence the survival of dairy cows milked once a day

ABSTRACT A particular emphasis has been put, by farmers, on the conformation and management of cows milked once a day (OAD). These factors might alter the culling decisions of herds after shifting from twice a day (TAD) to OAD milking. A Cox proportional hazard model was implemented to identify factors that influenced the survival of cows after the shift from TAD to OAD milking for three consecutive seasons (2013–2015). Overall, non-pregnant cows and those with low milk yield and low milk solids yield had a higher likelihood of being culled than more productive and pregnant cows. Holstein-Friesian and crossbred cows had a higher likelihood of being culled compared with Jerseys. Cows with better adaptability to milking (score > 7), and those with low pins/steeper rumps (score ≥ 4) and better udder support (score ≥ 6) were less likely to be culled. For traits such as body capacity and leg conformation, intermediate scores were associated with a lower likelihood of culling. Besides body capacity and udder support, traits including adaptability to milking, rump angle and leg conformation could also potentially be included in a new selection index for OAD dairy cattle.